(meth)acrylate, polymer and resist composition

ABSTRACT

A polymer contains a constituent unit having a specific acetal skeleton. This polymer is able to be used as a resist resin in DUV excimer laser lithography, electron beam lithography, EUV lithography, or the like.

CONTINUATION DATA

This application is a Continuation of U.S. application Ser. No.11/596,865, filed on Nov. 17, 2006, pending, which is a National Stageof PCT/JP05/08955, filed on May 17, 2005.

TECHNICAL FIELD

The present invention relates to a polymer which is useful as aconstituent component resin material of a positive resist, and a monomerwhich is useful as a raw material of a polymer for positive resist. Alsothe present invention relates to a resist composition using the polymer,and a pattern forming method, and, particularly, to a polymer forchemically amplified photoresist, which is suited for micro-processingusing excimer laser, electron beam, and X-ray.

BACKGROUND ART

Recently, in the field of micro-processing in the production ofsemiconductor devices and liquid crystal devices, fine patterning hasrapidly been developed with the progress of lithography technique. In atechnique for fine patterning, irradiation light having a shorterwavelength used. Specifically, ultraviolet ray typified by g-ray(wavelength: 438 nm) or i-ray (wavelength: 365 nm) used as conventionalirradiation light has been replaced by DUV (Deep Ultra Violet).

At present, a KrF excimer laser (wavelength: 248 nm) lithographytechnique is introduced in the market and a trial of introducing an ArFexcimer laser (wavelength: 193 nm) lithography technique, which isintended to realize shorter wavelength, has been made. Furthermore, a F₂excimer laser (wavelength: 157 nm) lithography technique has beenstudied as a next generation technique. As a lithography technique,which is slightly different from these techniques, an electron beamlithography technique and a EUV lithography technique has intensivelybeen studied.

As a high resolution resist to irradiation light having a shortwavelength or electron beam, a “chemically amplified photoresist”containing a photo acid generator is proposed and the chemicallyamplified photoresist are intensively improved and developed at present.In a chemically amplified positive resist, a dissolution rate to analkali developing solution of a polymer for resist must be increased byan action of an acid and a polymer having a structure, in whichhydrophilic groups are protected with acid-eliminating protectivegroups, is widely used. As a resist for ArF excimer laser lithography,patent document 1 discloses a polymer having, as a constituent unit, amonomer in which meth)acrylic acid is protected with an acid-eliminatingprotective group. Patent document 2 discloses a polymer containing aconstituent unit represented by the following formula (5).

in the general formula (5), R represents a hydrogen atom, a methylgroup, a linear or branched hydroxyalkyl group having 1 to 4 carbonatoms, or a linear or branched fluorinated alkyl group having 1 to 4carbon atoms; R³ each independently represents a monovalent alicyclichydrocarbon group having 4 to 20 carbon atoms or a derivative thereof,or a linear or branched alkyl group having 1 to 4 carbon atoms, and atleast one of R³(s) represents the alicyclic hydrocarbon group or aderivative thereof, or any two R³(s) are combined with each othertogether with carbon atoms attached thereto to form a divalent alicyclichydrocarbon group having 4 to 20 carbon atoms or a derivative thereof,and the remaining R³ represents a linear or branched alkyl group having1 to 4 carbon atoms or a monovalent alicyclic hydrocarbon group having 4to 20 carbon atoms or a derivative thereof; and U represents a divalentbridged hydrocarbon group having 5 to 12 carbon atoms.

However, in the case of preparing the (meth)acrylate for forming anacid-eliminating constituent unit represented by the general formula (5)described in patent document 2, the esterification reaction between(meth)acrylic acid having a bridged hydrocarbon group combined with acarboxyl group (structure U in the general formula (5)) and a tertiaryalcohol (C(R₃)₃OH) must be conducted. In this case, in order to increasereactivity of the esterification reaction, the esterification reactionmust be conducted after forming an acid anhydride of (meth)acrylic acidhaving a bridged hydrocarbon group combined with a carboxyl group, orreacting the (meth)acrylic acid having a bridged hydrocarbon groupcombined with a carboxyl group with thionyl chloride to form an acidchloride, and there was a problem such as a lot of reaction steps arerequired.

Patent document 1: Japanese Unexamined Patent Application, FirstPublication No. 2003-122007Patent document 2: Japanese Unexamined Patent Application, FirstPublication No. 2003 330192

PROBLEMS TO BE SOLVED BY THE INVENTION

An object of the present invention is to provide a (meth)acrylate whichcan introduce an acid-eliminating group by a simple method including fewreaction steps. Another object of the present invention is to provide apolymer using the (meth)acrylate, and a resist composition using thepolymer.

The present inventors have intensively studied so as to achieve theabove objects and found that a (meth)acrylate having a structure inwhich a specific ring structure is combined with an acetal-containingstructure is capable of introducing an acid-eliminating group by asimple method and the polymer is useful as a constituent component resinmaterial of a positive resist, and thus the present invention has beencompleted.

Namely, the first gist of the present invention lies in a polymercontaining a constituent unit represented by the following formula (1):

in the formula (1), R represents a hydrogen atom or a methyl group, R¹and R² each independently represents a hydrogen atom or an alkyl grouphaving 1 to 20 carbon atoms, or R¹ and R² are combined with each otherto form a ring structure; A¹ represents a single bond, alkylene,oxyalkylene, or —C(O)O— or —CH₂CH₂OC(O)—; A² represents a single bond,alkylene, oxyalkylene, —CO—, —C(O)O—, or —C(O)OCH₂CH₂—; and Z representsa cyclohexane ring, norbornane ring, bicyclo[2.2.2]octane ring, ortetracyclo[4.4.0.1^(2,5)]dodecane ring, all of which may have asubstituent.

The second gist of the present invention lies in the polymer, whereinthe formula (1) is a constituent unit represented by the followingformula (2):

in the formula (2), R represents a hydrogen atom or a methyl group, andR² represents an alkyl group having 1 to 20 carbon atoms.

The third gist of the present invention lies in a (meth)acrylaterepresented by the following formula (3):

in the formula (3), R, R¹, R², A¹, A² and Z are as defined in theformula (1).

The fourth gist of the present invention lies in the (meth)acrylate,wherein the formula (3) is represented by the following formula (4):

in the formula (4), R represents a hydrogen atom or a methyl group, R²represents an alkyl group having 1 to 20 carbon atoms, and n is 0 or 1.

The fifth gist of the present invention lies in a resist compositioncomprising the above polymer.

The sixth gist of the present invention lies in a pattern forming methodcomprising the steps of coating the above resist composition on ato-be-processed substrate, exposing the coated substrate to light havinga wavelength of 250 nm or less, and developing the exposed substrateusing a developing solution to form a pattern.

EFFECTS OF THE INVENTION

According to the present invention, it becomes possible to introduce anacid-eliminating group into a (meth)acrylate using a simple method byintroducing an acetal structure into a specific ring structure. Apolymer using the (meth)acrylate is useful as a positive resist.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the measurement results of ¹H-NMR of amethacrylate represented by the formula (A-1) obtained in Example 1.

FIG. 2 is a graph showing the measurement results of ¹H-NMR of amethacrylate represented by the formula (A-2) obtained in Example 3.

FIG. 3 is a graph showing the measurement results of mass spectrometryof a methacrylate represented by the formula (A-2) obtained in Example3.

FIG. 4 is a graph showing the measurement results of ¹H-NMR of amethacrylate represented by the formula (A-3) obtained in Example 5.

FIG. 5 is a graph showing the measurement results of mass spectrometryof a methacrylate represented by the formula (A-3) obtained in Example5.

BEST MODE FOR CARRYING OUT THE INVENTION 1. Polymer and Method forProducing the Polymer of the Present Invention

First, the polymer of the present invention will be described.

In the present invention, “(meth)acrylic acid” means methacrylic acid oracrylic acid.

The polymer of the present invention contains a constituent unitrepresented by the formula (1) and is particularly useful as a raw resinof a resist composition. The polymer of the present invention isexcellent in transparency to light having a wavelength of 250 nm or lessand therefore it can be used as a polymer for KrF resist, a polymer forArF resist and a polymer for F₂ resist, and can be particularlypreferably used as a polymer for ArF resist.

The polymer of the present invention contains a cyclohexane ring,norbornane ring, a bicyclo[2.2.2]octane ring, or atetracyclo[4.4.0.1^(2,5)]dodecane ring, all of which may have asubstituent, represented by Z in the formula (1). Examples of thesubstituent include, but are not limited to, linear or branched alkylgroup having 1 to 6 carbon atoms, which may have at least one groupselected from the group consisting of hydroxy group, carboxy group, acylgroup having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbonatoms, carboxy group esterified with an alcohol having 1 to 6 carbonatoms and amino group; hydroxy group; carboxy group; acyl group having 1to 6 carbon atoms; alkoxy group having 1 to 6 carbon atoms; carboxygroup esterified with an alcohol having 1 to 6 carbon atoms; or aminogroup. When the polymer contains a cyclic saturated hydrocarbon group,the resulting resist is excellent in etching resistance. The cyclicsaturated hydrocarbon group is preferably a norbornane ring or acyclohexane ring because the material is easily available, and ispreferably a bicyclo[2.2.2]octane ring or atetracyclo[4.4.0.1^(2,5)]dodecane ring in view of etching resistance.

The polymer of the present invention contains an acetal combined withthe cyclic saturated hydrocarbon group via a single bond, alkylene,oxyalkylene, —O—, —CO—, —C(O)O—, or —CH₂CH₂OC(O)—. The acetal isdecomposed in the presence of an acid catalyst to produce a carboxygroup or a hydroxy group. Utilizing the fact that solubility of theresin varies by this reaction, the polymer can be used in resistcompositions for metal etching, photo application, plate making,hologram, color filter, and phase difference film. The polymer can beparticularly preferably used in a chemically amplified positive resistusing a photo acid generator. Furthermore, when the polymer of thepresent invention is used as a raw resin of a positive resistcomposition, the resulting resist composition is excellent in line edgeroughness. The reason is considered as follows. Namely, when the acetalis decomposed under acidic conditions, physical properties other thansolubility of the resin cause less change than those of a conventionalpolymer for positive resist. When the polymer of the present inventionis used as a raw resin of the resist composition, trailing issuppressed. The reason is considered that the acetal is easilydecomposed by an acid.

In the present invention, a constituent unit represented by the formula(1) is a constituent unit represented by the following formula (2):

in the formula (2), R represents a hydrogen atom or a methyl group, andR² represents an alkyl group having 1 to 20 carbon atoms.

The polymer containing the constituent unit represented by the formula(2) is particularly preferable because the acetal structure has highthermostability and therefore the polymer is excellent in storagestability. The polymer is particularly preferable because of excellentline edge roughness. The reason is considered to be a carboxy groupprotected with an alkoxymethyl group. It is considered that, in the caseof the alkoxymethyl group, the size of a group eliminated under acidicconditions is comparatively smaller than that in the case of the otheracid-eliminating group such as tertiary ester group or alkoxyethyl groupand therefore physical properties other than solubility of the resincause less change. It is considered that the alkoxymethyl group has loweliminating energy as compared with an acid-eliminating group such astertiary ester group, which has conventionally been used in a chemicallyamplified positive resist, and suppresses the occurrence of trailing.

The polymer of the present invention can be produced by polymerizing a(meth)acrylate monomer represented by the following formula (3):

in the formula (3), R, R¹, R², A¹, A², and Z are as defined in theformula (1).

Specific examples of the monomer represented by the formula (3) includemonomers represented by the following formulas (3-1) to (3-91). In theformulas (3-1) to (3-91), R and Z are as defined in the formula (1).

Among these monomers, monomers represented by the formulas (3-10) to(3-14), (3-24) to (3-28), and (3-38) to (3-42) are preferable becausethey are excellent in etching resistance when used as the polymer forpositive resist, and monomers represented by the formulas (3-10),(3-11), (3-24), (3-25), (3-38), and (3-39) in which Z is abicyclo[2.2.2]octane ring are particularly preferable. Monomersrepresented by the formulas (3-5), (3-6), (3-8), (3-9), (3-19), (3-20),(3-22), (3-23), (3-33), (3-34), (3-36), and (3-37) in which Z is anorbornane ring, a bicyclo[2.2.2]octane ring, or atetracyclo[4.4.0.1^(2,5)]dodecane ring are particularly preferablebecause they cause less line edge roughness when used as the polymer forpositive resist, and monomers represented by the formulas (3-5), (3-6),(3-8), and (3-9) in which Z is a norbornane ring, a bicyclo[2.2.2]octanering, or a tetracyclo[4.4.0.1^(2,5)]dodecane ring are particularlypreferable.

In view of thermostability, monomers represented by the formulas (3-1),(3-43), (3-57), (3-64), and (3-71) to (3-77) are preferable, and themonomer represented by the following formula (4) is particularlypreferable:

in the formula (4), R represents a hydrogen atom or a methyl group, R²represents an alkyl group having 1 to 20 carbon atoms, and n is 0 or 1.

When the (meth)acrylate represented by the formula (4) is used as a rawmaterial of the polymer for positive resist, it tends to be excellent instorage stability because the acetal structure has high thermostability.The (meth)acrylate is particularly preferable because of excellent lineedge roughness. The reason is considered to be a carboxy group protectedwith an alkoxymethyl group. It is considered that, in the case of thealkoxymethyl group, the size of a group eliminated under acidicconditions is comparatively smaller than that in the case of the otheracid-eliminating group such as tertiary ester group or alkoxyethyl groupand therefore physical properties other than solubility of the resincause less change. It is considered that the alkoxymethyl group has loweliminating energy as compared with an acid-eliminating group such astertiary ester group, which has conventionally been used in a chemicallyamplified positive resist, and suppresses the occurrence of trailing.

In the (meth)acrylate represented by the formula (4), when n is 0, it isrepresented by the following formula (4A) and, when n is 1, it isrepresented by the following formula (4B):

in the formulas (1A) and (1B), R represents a hydrogen atom or a methylgroup, and R¹ represents an alkyl group having 1 to 20 carbon atoms.

Specific examples of the (meth)acrylate represented by the formulas (1A)and (1B) include (meth)acrylates represented by the following formulas(4A-1) to (4A-22) and (4B-1) to (4B-22).

In the formulas (4A-1) to (4A-22) and (4B-1) to (4B-22), R represents ahydrogen atom or a methyl group.

Among these (meth)acrylates, (meth)acrylates represented by the formulas(4A-7), (4A-8), (4A-20), and (4B-8) are preferable because of excellentsensitivity when formed into the polymer for resist, and (meth)acrylatesrepresented by the formulas (4A-1), (4A-2), (4B-1), and (4B-2) areparticularly preferable in view of excellent line edge roughness. Also(meth)acrylates represented by the formulas (4A-1) to (4A-22) and (4B-1)to (4B-22) have sometimes two or more position isomers and stereoisomersrepresented by the following formulas (4A-a) to (4A-h) and (4B-a) to(4B-x), and optical isomers thereof.

Among these isomers, (meth)acrylate represented by the formulas (4A) and(4B) may be an isomer alone, or a mixture of two or more isomers.

The monomers of the present invention can be produced, for example, bythe following methods. The following steps (I) to (IV) are examples ofthe production steps of monomers represented by the formulas (3-22),(3-24), (3-5), and (3-46), and similar monomers other than thesemonomers can also be produced by the same steps.

In the steps (I) and (II), norbornenecarboxylic acid and norbornenealcohol as raw materials can be synthesized by a known method, andcommercially available products can also be used. The addition reactionof acrylic acid or methacrylic acid to nornenecarboxylic acid andnorbornene alcohol is preferably conducted in the absence of a solventor the presence of a solvent such as toluene, using an acid catalyst andusing excess acrylic acid or methacrylic acid. Examples of the acidcatalyst used in the addition reaction include, but are not limited to,hydrochloric acid, sulfuric acid, nitric acid, p-toluenesulfonic acid,methanesulfonic acid, acetic acid, trifluoroacetic acid, andtrifluoromethanesulfonic acid. In view of the reaction rate, sulfuricacid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid arepreferable, and trifluoromethanesulfonic acid is more preferable. Theaddition reaction of carboxylic acid or alcohol to vinylether ispreferably conducted in a solvent such as toluene or tetrahydrofuranusing an acid catalyst.

In the step (III), commercially available terpinene as a raw materialcan be used. The cyclic addition reaction of terpinene and acrylic acideasily proceeds by a known method, and is preferably conducted in theabsence of a solvent or the presence of a solvent such as methanol usinga catalyst such as Lewis acid, if necessary. The subsequent additionreaction of acrylic acid or methacrylic acid and the addition reactionto vinylether can be used in the same manner as in the steps (I) and(II).

In the step (IV), commercially available hydroxyethyl methacrylate,hexahydrophthalic anhydride, and 2,3-dihydropyran as raw materials canbe used. The reaction of ring-opening addition reaction of hydroxyethylmethacrylate to hexahydrophthalic anhydride easily proceeds by a knownmethod and is preferably conducted in the absence of a solvent or thepresence of a solvent such as methanol using a catalyst such as Lewisacid, if necessary. The subsequent addition reaction of carboxylic acidto 2,3-dihydropyran can be used in the same manner as in the steps (I)and (II).

(meth)acrylates represented by the formula (4A) and (4B) can be producedin the same manner as in the steps (V) and (VI).

In the steps (V) and (VI), norbornenecarboxylic acid andtetracyclo[4.4.0.1^(2,5)]dodecenecarboxylic acid as raw materials may besynthesized by a known method, and commercially available products maybe used.

The first step is the addition step of (meth)acrylate tonorbornenecarboxylic acid or tetracyclo[4.4.0.1^(2,5)]dodecenecarboxylicacid. When the addition reaction of (meth)acrylic acid is conducted,excess (meth)acrylic acid is preferably used relative tonorbornenecarboxylic acid or tetracyclo[4.4.0.1^(2,5)]dodecenecarboxylicacid in view of the reaction rate. The amount of the (meth)acrylic acidis preferably 2 mol or more, and more preferably 3 mol or more, based on1 mol of norbornenecarboxylic acid ortetracyclo[4.4.0.1^(2,5)]dodecenecarboxylic acid. The amount of the(meth)acrylic acid is preferably 15 mol or less, and more preferably 8mol or less. When the amount is less than the above range, the reactionmay not proceed sufficiently. On the other hand, when the amount is morethan the above range, it may become difficult to remove excess(meth)acrylic acid after the reaction.

The addition reaction of the (meth)acrylic acid is usually conducted inthe presence of an acid catalyst. Examples of the acid catalyst includeLewis acid such as boron trifluoride; mineral acid such as sulfuricacid, hydrochloric acid, nitric acid, or phosphoric acid; organic acidsuch as p-toluenesulfonic acid, benzenesulfonic acid,dodecylbenzenesulfonic acid, methanesulfonic acid, camphorsulfonic acid,or trifluoromethanesulfonic acid; heteropoly acid such asphosphotungstic acid or tungstosilicic acid; and strong acidicion-exchange resin. Among these acid catalysts, sulfuric acid,p-toluenesulfonic acid, camphorsulfonic acid, methanesulfonic acid, andtrifluoromethanesulfonic acid are preferable because of high reactivity,and methanesulfonic acid is particularly preferable because of easyhandling. The amount of the acid catalyst is preferably 0.03 mol ormore, more preferably 0.05 mol or more, preferably 0.3 mol or less, andmore preferably 0.25 mol or less, based on 1 mol of norbornenecarboxylicacid. When the amount is less than the above range, the acid additionreaction may not proceed sufficiently. On the other hand, when theamount is more than the above range, it may become difficult to conductpurification after the acid addition reaction. The temperature at whichthe acid addition reaction is conducted is preferably 50° C. or higher,more preferably 70° C. or higher, preferably 180° C. or lower, and morepreferably 150° C. or lower. When the temperature is lower than theabove range, the reaction may not proceed sufficiently. On the otherhand, when the temperature is further lower the above range, by-productmay increase.

Examples of the solvent used in the acid addition reaction include, butare not limited to, ether-based solvents such as tetrahydrofuran,tetrahydropyran, dimethylether, diethylether, diisopropylether, andmethyl-t-butylether; aliphatic hydrocarbon-based solvents such aspentane, hexane, heptane, octane, and cyclohexane; and aromatichydrocarbon-based solvents such as benzene, toluene, and xylene. It ispreferred that these solvents are preliminarily dehydrated by aconventional method because high reaction yield is obtained. The acidaddition reaction can also be conducted in the absence of a solvent andgood yield can be attained. Therefore, the acid addition reaction ispreferably conducted in the absence of a solvent.

The time of the acid addition reaction varies depending on the batchsize, acid catalyst, and reaction conditions, but is preferably 1 houror more and 12 hours or less. More preferably, the time is 2 hours ormore and 8 hours or less. When the time is less than the above range,the reaction may not proceed sufficiently. On the other hand, when thetime is more than the above range, by-product may increase.

When the acid addition reaction is conducted, the polymerizationsometimes occurs and therefore a polymerization inhibitor is preferablyadded. The polymerization inhibitor is not specifically limited as longas it can suppress the polymerization, and examples thereof includehydroquinone, hydroquinone monomethyl ether,2,4-dimethyl-6-t-butylphenol, p-benzoquinone,2,5-diphenyl-p-benzoquinone, phenothiazine, N-nitrosodiphenylamine,copper salt, metallic copper, and 2,2,6,6-tetramethylpiperidine-1-oxyl.It is also effective to suppress the polymerization by reacting whilebubbling an air or oxygen.

After the completion of the acid addition reaction, the acid catalystcan be removed by a method of removing an acid catalyst by washing orneutralizing and washing the reaction solution with an aqueous alkalisolution of sodium hydroxide, potassium hydroxide, sodium carbonate,sodium hydrogen carbonate, or the like; a method of removing an acidcatalyst by adding an alkali powder of sodium carbonate, sodium hydrogencarbonate, magnesium oxide, or the like, followed by stirring andfurther filtration of a neutral salt; or a method of neutralizing anacid catalyst by adding an amine such as triethylamine, triethanolamine,morpholine, or the like. Among these methods, a method of washing withan aqueous alkali solution and extracting with an organic solvent ispreferable because the acid catalyst can be effectively removed.Examples of the organic solvent, which can be used for reaction, includetoluene, benzene, hexane, cyclohexane, ethyl acetate, diethylether, anddiisopropylether. Among these solvents, toluene, ethyl acetate, anddiethylether are preferable because extraction efficiency is high andthe amount of the solvent can be decreased, and toluene is particularlypreferable because purity of the objective compound can be increased.

The resulting (meth)acrylic acid adduct may be purified by a knownmethod such as distillation or column chromatography, and may be used inthe following step without being purified. Since the (meth)acrylic acidadduct may be polymerized by heating, purification is not preferablyconducted because the entire yield increases.

The following step is an alkoxymethyletherification step of a carboxygroup of a (meth)acrylic acid adduct. The alkoxymethyletherification isconducted by reacting the (meth)acrylic acid adduct with a halogenatedalkylether or dialkoxymethane in the presence of a base. Also the(meth)acrylic acid adduct may be reacted with formaldehyde and analcohol may be reacted. In view of the reaction rate, it is preferred toreact with a halogenated alkylether. Because of less by-product,chloroalkylether is particularly preferable. The base is notspecifically limited, and triethylamine, diisopropylethylamine,pyridine, dimethylaminopyridine, sodium hydride, lithium hydride,potassium t-butoxide, sodium methoxide, and sodium ethoxide are used.The reaction solvent is not specifically limited, but a polar solventsuch as methanol, ethanol, tetrahydrofuran, formamide, acetamide,dimethyl formamide, dimethyl acetamide, or dimethyl sulfoxide arepreferably used in view of the reaction rate, and dimethyl formamide isparticularly preferable. The temperature at which thealkoxymethyletherification is conducted is preferably −50° C. or higher,more preferably 0° C. or higher, preferably 100° C. or lower, and morepreferably 50° C. or lower. When the temperature is lower than the aboverange, the reaction may not proceed sufficiently. On the other hand,when the temperature is further lower than the above range, by-productmay increase.

The resulting (meth)acrylate of the present invention can be used as araw material of the polymer without being purified, but it is preferablypurified so as to suppress contamination of the polymer with impurities.The purification can be conducted by a known method such as columnchromatography, distillation, or recrystallization, and is preferablyconducted by distillation because of easy handling. Since thepolymerization sometimes occurs during the distillation, apolymerization inhibitor is preferably added. The polymerizationinhibitor is not specifically limited as long as it suppresses thepolymerization, and examples thereof include hydroquinone,hydroquinonemonomethylether, 2,4-dimethyl-6-t-butylphenol,p-benzoquinone, 2,5-diphenyl-p-benzoquinone, phenothiazine,N-nitrosodiphenylamine, copper salt, metallic copper,2,2,6,6-tetramethylpiperidine-1-oxyl. It is also effective to suppressthe polymerization by distillation while bubbling an air or oxygen.

When heated during distillation, the (meth)acrylate of the presentinvention is sometimes decomposed. The reason is considered that anacidic component used in the reaction remains and elimination of anacid-eliminating group occurs. In order to suppress the decomposition,distillation may be conducted by adding a base. The base is notspecifically limited, but is preferably sodium hydroxide or potassiumhydroxide because of easy handling.

The (meth)acrylate of the present invention can be produced according tothe scheme shown in the following steps (VII) and (VIII).

The first step is an alkoxymethyletherification step ofnorbornenecarboxylic acid or tetracyclo[4.4.0.1^(2,5)]dodecenecarboxylicacid. The alkoxymethyletherification is conducted by reactingnorbornenecarboxylic acid with a halogenated alkylether ordialkoxymethane in the presence of a base. Also the (meth)acrylic acidadduct, and formaldehyde and an alcohol may be reacted.

The second step is a hydroxylation step to an alkoxymethyletherifiedcompound. The alkoxymethyletherified compound, and formic acid and aBH₃-tetrahydrofuran complex are reacted and then hydrolyzed with a basesuch as sodium carbonate to obtain an alcohol compound.

Furthermore, the resulting alcohol compound and (meth)acrylic acidchloride are dehydrochlorinated in the presence of a base such as sodiumhydroxide to obtain a (meth)acrylate of the present invention.

Also it can be produced according to the scheme shown in the followingsteps (IX) and (X) in which the step order was replaced as compared withthe steps (VII) and (VIII).

The products of the steps (I) to (X) sometimes contain some positionalisomers, geometrical isomers, and optical isomers. As the raw materialof the constituent unit (1) of the polymer of the present invention, amixture of two or more kinds of isomers may be used, or any isomer maybe used alone after the purification. Therefore, the mixture of isomerscan be used for the polymerization reaction as it is. Even if themixture contains a reaction intermediate, it can be used for thepolymerization reaction as it is. The product of the reaction may bepurified by simple distillation, thin film distillation,recrystallization, or column chromatography, if necessary.

The polymer of the present invention may be a homopolymer or acopolymer.

When the polymer of the present invention is used as a positive resistmaterial, it is preferred to copolymerize a monomer represented by theformula (3) of the present invention with compounds represented by thefollowing formulas (6-1) to (6-80) because of excellent resistperformances such as sensitivity, resolution, and etching resistance. Asthe copolymerizable component, any monomer can be used according to thepurposes and also a copolymerization ratio may be decided according tothe purposes. In the formulas (6-1) to (6-80), R represents a hydrogenatom or a methyl group.

The monomers described above can be used alone or in combination, ifnecessary.

When the polymer of the present invention is used as a resistcomposition, the proportion of the constituent unit represented by theformula (1) in the polymer is preferably from 20 to 60 mol %, and morepreferably from 30 to 50 mol %, because of excellent sensitivity andresolution, and small line edge roughness.

In view of excellent sensitivity and resolution, a monomer representedby the formula (3) is preferably copolymerized with one or more monomersselected from the group consisting of monomers represented by theformulas (6-1), (6-2), (6-16), (6-57), (6-58), and (6-65) to (6-67). Thepolymer obtained by copolymerizing these monomers is made soluble in analkali developing solution by decomposing through an action of an acid.Therefore, a positive resist using the polymer is excellent insensitivity and resolution.

In view of excellent substrate adhesion, a monomer represented by theformula (3) is preferably copolymerized with one or more monomersselected from the group consisting of monomers represented by theformulas (6-23), (6-24), (6-28), (6-29), (6-36), (6-47), (6-59), and(6-63). These monomers have a lactone structure in the molecule and apolymer obtained by copolymerizing these monomers is excellent insubstrate adhesion.

Because of excellent pattern shape, a monomer represented by the formula(3) is preferably copolymerized with one or more monomers selected fromthe group consisting of monomers represented by the formulas (6-19) and(6-74). A positive resist using a polymer containing alicyclic skeletonhaving a hydroxy group or a cyano group is excellent in pattern shape.

In view of excellent etching resistance, a monomer represented by theformula (3) is preferably copolymerized with one or more monomersselected from the group consisting of monomers represented by theformulas (6-22) and (6-64).

Among the copolymers described above, a copolymer comprising 25 to 70mol % of a constituent unit represented by the formula (1), 25 to 70 mol% of a constituent unit derived from one or more monomers selected fromthe group consisting of monomers represented by the formulas (6-23),(6-24), (6-28), (6-29), (6-36), (6-47), (6-59), and (6-63), 5 to 20 mol% of a constituent unit derived from one or more monomers selected fromthe group consisting of monomers represented by the formulas (6-19) and(6-74) is particularly excellent in view of excellent sensitivity,resolution, and line edge roughness.

In the polymer of the present invention, each constituent unit can takeoptional sequence. Therefore, the polymer of the present invention maybe a random copolymer, an alternating copolymer, or a block copolymer.

The monomer represented by the formula (3) can also be copolymerizedwith the other monomer. Specific examples thereof include(meth)acrylates having a linear or branched structure, such as methyl(meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,n-propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate,isobutyl (meth)acrylate, t-butyl (meth)acrylate, methoxymethyl(meth)acrylate, n-propoxyethyl (meth)acrylate, i-propoxyethyl(meth)acrylate, n-butoxyethyl (meth)acrylate, i-butoxyethyl(meth)acrylate, t-butoxyethyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxy-n-propyl(meth)acrylate, 4-hydroxy-n-butyl (meth)acrylate, 2-ethoxyethyl(meth)acrylate, 1-ethoxyethyl (meth)acrylate, 2,2,2-trifluoroethyl(meth)acrylate, 2,2,3,3-tetrafluoro-n-propyl (meth)acrylate,2,2,3,3,3-pentafluoro-n-propyl (meth)acrylate, methylα-(tri)fluoromethyl acrylate, ethyl α-(tri)fluoromethyl acrylate,2-ethylhexyl α-(tri)fluoromethyl acrylate, n-propyl α-(tri)fluoromethylacrylate, i-propyl α-(tri)fluoromethyl acrylate, n-butylα-(tri)fluoromethyl acrylate, i-butyl α-(tri)fluoromethyl acrylate,t-butyl α-(tri)fluoromethyl acrylate, methoxymethyl α-(tri)fluoromethylacrylate, and ethoxyethyl α-(tri)fluoromethyl acrylate; aromatic alkenylcompounds such as styrene, α-methylstyrene, vinyltoluene,p-hydroxystyrene, p-t-butoxycarbonylhydroxystyrene,3,5-di-t-butyl-4-hydroxystyrene, 3,5-dimethyl-4-hydroxystyrene,p-t-perfluorobutylstyrene, and p-(2-hydroxy-i-propyl)styrene;unsaturated carboxylic acids and carboxylic danhydrides, such as(meth)acrylic acid, maleic acid, maleic anhydride, itaconic acid, anditaconic anhydride; and ethylene, propylene, norbornene,tetrafluoroethylene, acrylamide, N-methylacrylamide,N,N-dimethylacrylamide, vinyl chloride, ethylene, vinyl fluoride,vinylidene fluoride, tetrafluoroethylene, and vinyl pyrrolidone.

The mass average molecular weight of the polymer of the presentinvention is not specifically limited, and is preferably 1,000 or more,and more preferably 1,000,000 or less. When the polymer of the presentinvention is used as a positive resist material, the mass averagemolecular weight of the polymer is preferably 1,000 or more, morepreferably 2,000 or more, and particularly preferably 5,000 or more inview of etching resistance and resist shape. The mass average molecularweight of the polymer of the present invention is preferably 100,000 orless, more preferably 50,000 or less, and particularly preferably 20,000or less in view of solubility and resolution to a resist solution.

The polymer of the present invention can be produced by polymerizing amonomer represented by the formula (3). Examples of the polymerizationmethod include radical polymerization, anion polymerization, and cationpolymerization methods. When it is necessary to control the molecularweight, molecular weight distribution, and stereoregularity, apolymerization method referred to precision polymerization typified byliving polymerization.

In general, examples of the production process for obtaining a polymerinclude bulk polymerization process, suspension polymerization process,emulsion polymerization process, vapor phase polymerization process, andsolution polymerization process. These production processes may beappropriately decided according to properties of the objective polymer.It is necessary to remove the monomer remained after the completion ofthe polymerization reaction and the molecular weight of the copolymer iscomparatively decreased so as not to decrease light transmittance andtherefore a solution polymerization process among the above processes isoften employed. Among the solution polymerization processes, a droppolymerization method of adding dropwise a monomer solution, which isprepared by preliminarily dissolving a monomer and a polymerizationinitiator in an organic solvent, in an organic solvent maintained at afixed temperature is preferably employed because the average molecularweight and molecular weight distribution slightly vary with the kind ofa production batch and a reproducible copolymer is easily obtained.

The polymer of the present invention is usually obtained by polymerize amonomer solution containing a monomer represented by the formula (3) inthe presence of a polymerization initiator. In the polymerization usinga polymerization initiator, first, a radical compound of apolymerization initiator is produced in the reaction solution and chainpolymerization of the monomer proceeds in the presence of this radicalcompound as an origin.

The polymerization initiator used in the production of the polymer ofthe present invention is preferably a polymerization initiator whichefficiently generates a radical by heat. Examples of the polymerizationinitiator include azo compounds such as 2,2′-azobisisobutyronitrile anddimethyl-2,2′-azobisisobutyrate; and organic peroxides such as2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

When the polymer of the present invention is produced, a chain transferagent may be used. A polymer having a low molecular weight and smallmolecular weight distribution can be produced by using the chaintransfer agent. Examples of preferable chain transfer agents include1-butanethiol, 2-butanethiol, 1-octanethiol (n-octylmercaptan),1-decanethiol, 1-tetradecanethiol, cyclohexanethiol,2-methyl-1-propanethiol, 2-mercaptoethanol, mercaptoacetic acid, and1-thioglycerol.

The amount of the polymerization initiator is not specifically limited,but is preferably from 1 to 20 mol % based on the entire amount of themonomer used. The amount of the chain transfer agent is not specificallylimited, but is preferably from 1 to 20 mol % based on the entire amountof the monomer used.

The polymerization temperature is not specifically limited, but ispreferably 50° C. or higher and 150° C. or lower.

When the monomer, the polymerization initiator and the resultingpolymer, and the chain transfer agent are used in combination, theorganic solvent used in the solution polymerization process ispreferably a solvent capable of dissolving any chain transfer agent.Examples of the organic solvent include 1,4-dioxane, isopropyl alcohol,acetone, tetrahydrofuran (hereinafter also referred to as “THF”), methylisobutyl ketone, γ-butyrolactone, and propylene glycol monomethyl etheracetate (hereinafter also referred to as “PGMEA”), and ethyl lactate.

The polymer solution produced by the method such as solutionpolymerization may be optionally purified by diluting with a goodsolvent such as 1,4-dioxane, acetone, THF, methyl isobutyl ketone,γ-butyrolactone, PGMEA, or ethyl lactate to obtain a solution havingproper viscosity, and adding dropwise the solution in a large amount ofa poor solvent such as methanol or water, thereby precipitating apolymer. This step is generally referred to as a reprecipitation stepand is very effective to remove the unreacted monomer and thepolymerization initiator remained in the polymerization solution. Theprecipitate was filtered and sufficiently dried to obtain a polymer ofthe present invention. After filtration, a wet powder can be usedwithout being dried.

2. Resist Composition of the Present Invention

The resist composition of the present invention will now be described.

The resist composition of the present invention is obtained bydissolving the polymer of the present invention in a solvent. Thechemically amplified photoresist composition of the present invention isobtained by dissolving the polymer of the present invention and thephoto acid generator in a solvent. The chemically amplified positiveresist is excellent in sensitivity. These polymers of the presentinvention may be used alone or in combination. The polymer of thepresent invention may be used as a blend polymer mixed with the otherpolymer. The polymer solution can be used as it is in a resistcomposition without separating a polymer from the polymer solutionthrough solution polymerization. Alternatively, this polymer solutioncan be used in the resist composition after being diluted with asuitable solvent. The resist composition of the present invention maycontain a polymer other than the polymer of the present invention.

In the resist composition of the present invention, the solvent capableof dissolving the polymer of the present invention can be optionallyselected.

Examples of the solvent include linear or branched ketones such asmethyl ethyl ketone, methyl isobutyl ketone, and 2-pentanone; cyclicketones such as cyclopentanone and cyclohexanone; propylene glycolmonoalkyl acetates such as propylene glycol monomethyl ether acetate;ethylene glycol monoalkyl ether acetates such as ethylene glycolmonomethyl ether acetate; propylene glycol monoalkyl ethers such aspropylene glycol monomethyl ether; ethylene glycol monoalkyl ethers suchas ethylene glycol monomethyl ether; diethylene glycol alkyl ethers suchas diethylene glycol dimethyl ether; esters such as ethyl acetate andethyl lactate; alcohols such as n-propyl alcohol, isopropyl alcohol,n-butyl alcohol, and tert-butyl alcohol; 1,4-dioxane, ethylenecarboxylate, and γ-butyrolactone. These solvents may be used alone or incombination.

The content of the solvent is preferably 200 parts by mass or more, andmore preferably 300 parts by mass or more, based on 100 parts by mass ofthe polymer for resist. The content of the solvent is preferably 5,000parts by mass or less, and more preferably 2,000 parts by mass or less,based on 100 parts by mass of the polymer for resist.

When the polymer of the present invention is used in a chemicallyamplified positive resist, it is necessary to use a photo acidgenerator.

The photo acid generator contained in the chemically amplifiedphotoresist composition of the present invention can be optionallyselected from those which can be used as an acid generator of thechemically amplified photoresist composition. These photo acidgenerators may be used alone or in combination.

Examples of the photo acid generator include onium salt compounds,sulfonimide compounds, sulfone compounds, sulfonate compounds,quinonediazide compounds, and diazomethane compounds. As the photo acidgenerator, onium salt compounds such as sulfonium salt, iodonium salt,phosphonium salt, diazonium salt, and pyridinium salt are preferable,and specific examples thereof include triphenylsulfonium triflate,triphenylsulfonium hexafluoroantimonate, triphenylsulfoniumnaphthalenesulfonate, (hydroxyphenyl)benzylmethylsulfoniumtoluenesulfonate, diphenyliodonium triflate, diphenyliodoniumpyrenesulfonate, diphenyliodonium dodecylbenzenesulfonate,diphenyliodonium hexafluoroantimonate, p-methylphenyldiphenylsulfoniumnonafluorobutanesulfonate, and tri(tert-butylphenyl)sulfoniumtrifluoromethanesulfonate.

The content of the photo acid generator is appropriately decidedaccording to the kind of the selected photo acid generator, and ispreferably 0.1 parts by mass or more, and more preferably 0.5 parts bymass or more, based on 100 parts by mass of the polymer for positiveresist. By adjusting the content of the photo acid generator within theabove range, it is possible to sufficiently cause the chemical reactionthrough a catalytic action of the acid generated under exposure. Thecontent of the photo acid generator is preferably 20 parts by mass orless, and more preferably 10 parts by mass or less, based on 100 partsby mass of the polymer for positive resist. By adjusting the content ofthe photo acid generator within the above range, stability of the resistcomposition is improved and the occurrence of coating unevenness in thecase of coating the composition and scum on development is sufficientlysuppressed.

Furthermore, the chemically amplified photoresist composition of thepresent invention can be mixed with a nitrogen-containing compound. Bymixing the nitrogen-containing compound, resist pattern shape and postexposure stability of the latent image formed by the pattern wiseexposure of the resist layer are further improved. Namely, the resultingresist pattern has nearly rectangular profile. Although a resist film isexposed, subjected to post exposure baking (PEB) and then allowed tostand for several hours before the following development treatment in amass production line of semiconductors, deterioration of the resistpattern profile caused when the resist film is allowed to stand (with alapse of time) is more suppressed.

As the nitrogen-containing compound, any known nitrogen-containingcompound can be used. Among these nitrogen-containing compounds, anamine is preferable, and a secondary lower aliphatic amine and atertiary lower aliphatic amine are more preferable.

As used herein, “lower aliphatic amine” means an amine of an alkyl oralkyl alcohol having 5 carbon atoms or less.

Examples of the secondary lower aliphatic amine and the tertiary loweraliphatic amine include trimethylamine, diethylamine, triethylamine,di-n-propylamine, tri-n-propylamine, tripentylamine, diethanolamine, andtriethanolamine. As the nitrogen-containing compound, a tertiaryalkanolamine such as triethanolamine is more preferable.

These nitrogen-containing compounds may be used alone or in combination.The content of the nitrogen-containing compound is appropriately decidedaccording to the kind of the selected nitrogen-containing compound, butis preferably 0.01 parts by mass or more based on 100 parts by mass ofthe polymer for positive resist. By adjusting the content of thenitrogen-containing compound within the above range, the resultingresist pattern shape can have nearly rectangular profile. The content ofthe nitrogen-containing compound is preferably 2 parts by mass or lessbased on 100 parts by mass of the polymer for positive resist. Byadjusting the content of the nitrogen-containing compound within theabove range, deterioration of sensitivity can be suppressed.

The chemically amplified photoresist composition of the presentinvention can also be mixed with an organic carboxylic acid, oxo acid ofphosphorus, or a derivative thereof. By mixing with these compounds,deterioration of sensitivity caused by mixing the nitrogen-containingcompound can be prevented, and also resist pattern shape and postexposure stability of the latent image formed by the pattern wiseexposure of the resist layer are further improved.

As the organic carboxylic acid, for example, malonic acid, citric acid,malic acid, succinic acid, benzoic acid, and salicylic acid arepreferable. Examples of the oxo acid of phosphorus, or derivativethereof include phosphoric acid and derivative thereof such as ester,for example, phosphoric acid, di-n-butyl phosphate, or diphenylphosphate; phosphonic acid and derivative thereof such as ester, forexample, phosphonic acid, dimethyl phosphonate, di-n-butyl phosphonate,phenylphosphonate, diphenyl phosphonate, or dibenzyl phosphonate;phosphinic acid and derivative thereof such as ester, for example,phosphinic acid or phenyl phosphinate. Among these, phosphonic acid ispreferable.

These compounds (organic carboxylic acid, oxo acid of phosphorus, orderivative thereof) may be used alone or in combination.

The content of these compounds (organic carboxylic acid, oxo acid ofphosphorus, or derivative thereof) is appropriately decided according tothe kind of the selected compound, but is preferably 0.01 parts by massor more based on 100 parts by mass of the polymer for resist. Byadjusting the content of these compounds within the above range, theresulting resist pattern shape can have nearly rectangular profile. Thecontent of these compounds (organic carboxylic acid, oxo acid ofphosphorus, or derivative thereof) is preferably 5 parts by mass or lessbased on 100 parts by mass of the polymer for resist. By adjusting thecontent of these compounds within the above range, thickness loss of theresist pattern can be reduced.

The chemically amplified photoresist composition of the presentinvention can contain either of a nitrogen-containing compound, and atleast one selected from the group consisting of an organic carboxylicacid, oxo acid of phosphorus and a derivative thereof, or can containonly one of them.

Furthermore, the resist composition of the present invention can containvarious additives such as surfactants, quenchers other than thenitrogen-containing compound, sensitizers, antihalation agents, storagestabilizers, and defoamers, if necessary. These additives can be used aslong as they are known in this field. The amount of these additives isnot specifically limited and may be appropriately decided.

The polymer for positive resist of the present invention may be used asresist compositions for metal etching, photofabrication, plate making,hologram, color filter, and phase difference film.

3. Method for Producing Pattern of the Present Invention

Subsequently, an example of a pattern forming method of the presentinvention will be described.

First, the resist composition of the present invention is coated on thesurface of a to-be-processed substrate such as silicone wafer, on whicha pattern is formed, by spin coating. The to-be-processed substratecoated with the resist composition is dried by a baking treatment(prebaking) to form a resist film on the substrate.

Then, the resist film thus obtained is exposed to light having awavelength of 250 nm or less through a photomask (exposure). Light usedin exposure is preferably KrF excimer laser, ArF excimer laser or F₂excimer laser, and particularly preferably ArF excimer laser. It ispreferred to expose to electron beam.

After the exposure, the exposed substrate is subjected to a heattreatment (post exposure baking, PEB) and dipped in an alkali developingsolution, thereby dissolving the exposed are in the developing solution(development). The alkali developing solution to be used may be any onewhich is known. After the development, the substrate is appropriatelyrinsed with pure water or the like. Thus, a resist pattern is formed onthe to-be-processed substrate.

Usually, the to-be-processed substrate with a resist pattern formedthereon is appropriately subjected to a heat treatment (postbaking)thereby reinforcing the resist, and the resist free area is selectivelyetched. After the etching, the resist is usually removed by a remover.

EXAMPLES

The present invention will now be described in detail by way ofexamples, but the present invention is not limited thereto.

In the examples and comparative example, the measurement of physicalproperties of the polymer and the evaluation of the resist wereconducted by the following procedures.

<Weight Average Molecular Weight of Polymer>

About 20 mg of a polymer was dissolved in 5 mL of THF, followed byfiltration with a 0.5 μm membrane filter to prepare a sample solution.Using the sample solution, weight average molecular weight of thepolymer was measured by gel permeation chromatography (GPC) manufacturedby Tosoh Corporation. Using three separation columns manufactured bySHOWA DENKO K.K. under the trade name of Shodex GPC K-805L arranged inseries, and using THF as a solvent, the measurement was conducted underthe conditions of a flow rate of 1.0 mL/min, a measuring temperature of40° C. and a charge amount of 0.1 mL. A differential refractometer wasused as a detector and polystyrene was used as a standard polymer.

<Thermostability of Acetal Structure of Polymer>

Thermostability of a polymer was determined by the following procedure.Namely, 3.0 g of the polymer was heated with stirring in a test tube at100° C. for 4 hours using Personal Organic Synthesizer, ChemiStationPPS-2510 manufactured by TOKYO RIKAKIKAI CO., LTD. and then ¹H-NMR wasmeasured before and after heating with stirring. This measurement wasconducted by the following procedure. Namely, a about 5 mass % solutionof a polymer for positive resist sample in deuterated choloroform,deuterated acetone, or deuterated dimethyl sulfoxide was charged in atest tube having a diameter of 5 mmφ and the measurement was conductedunder the conditions of a measuring temperature of 40° C., a measuringfrequency of 270 MHz, and a single pass mode 64 times using an apparatusmanufactured by JEOL Ltd. under the trade name of JN GX-270 modelFT-NMR.

Thermostability was evaluated by the degree of change in a proportion ofhydrogen combined with carbon interposed between oxygen and oxygen ofthe acetal structure.

Thermostability index={(integrated value of hydrogen combined withcarbon interposed between oxygen and oxygen after thermal decompositiontest)/(total integrated value between chemical shift δ values of 0 to2.6 ppm after thermal decomposition test)}/{(integrated value ofhydrogen combined with carbon interposed between oxygen and oxygenbefore thermal decomposition test)/(total integrated value betweenchemical shift δ values of 0 to 2.6 ppm before thermal decompositiontest)}

The closer a thermostability index gets to 1, the higher thermostabilityof the acetal becomes. When the thermostability index is less than 1,thermostability of the acetal is low.

Example 1 Synthesis of Methacrylate Represented by the Following Formula(A-1)

In a 1 L glass three-necked flask equipped with a stirrer, athermometer, and a reflux condenser tube, 69.0 g (0.50 mol) ofnorbornenecarboxylic acid, 129.0 g (1.5 mol) of methacrylic acid, and4.8 g (0.05 mol) of methanesulfonic acid were charged and thetemperature was raised to 130° C. while stirring. While maintaining thetemperature of the flask at 130° C., the reaction was conducted for 2hours. After the completion of the reaction, the reaction solution wascooled in an ice bath and then 200 ml of toluene and 100 ml of waterwere added while stirring. The solution was transferred to a separatoryfunnel and, after removing the aqueous layer, the toluene layer wasconcentrated to obtain 110.0 g of a methacrylic acid adduct of thefollowing formula (7).

110.0 g of the resulting methacrylic acid adduct represented by theformula (7) and 73.7 g (0.74 mol) of butyl vinyl ether were charged in a300 ml glass three-necked flask equipped with a stirrer, a thermometerand a reflux condenser tube, the temperature was raised to 100° C. whilestirring. While maintaining the temperature of the flask at 100° C., thereaction was conducted for 3 hours and a half. Disappearance of themethacrylic acid adduct was confirmed by gas chromatography andproduction of a methacrylate represented by the formula (A-1) wasconformed by H¹-NMR. After the completion of the reaction, the ester wascooled to room temperature to obtain a crude product (A-1).

To purify the crude product (A-1) by distillation, it was heated to 160°C. using an oil bath and a fraction at an overhead temperature of 108°to 145° C. was separated at a vacuum degree of 26.6 to 79.8 Pa. However,thermal decomposition occurred during distillation and the separatedfraction was a methacrylic acid adduct as the raw material and thereforepurification by distillation could not be conducted. Therefore, in thefollowing operation, the crude product (A-1), which is not purified bydistillation after the completion of the reaction, was used as themethacrylate represented by the formula (A-1).

Example 2 Synthesis of Copolymer P-1

In a flask equipped with a nitrogen introducing tube, a stirrer, acondenser and a thermometer, 22.4 parts of propylene glycol monomethylether acetate (hereinafter referred to as PGMEA) was charged under anitrogen atmosphere and the temperature of a hot water bath was raisedto 80° C. while stirring. From a dropping apparatus containing a monomersolution prepared by mixing 14.3 parts of a methacrylate, 7.5 parts of amonomer represented by the following formula (hereinafter referred to asGBLMA) represented by the formula (A-1):

5.2 parts of HAdMA represented by the following formula:

40.4 parts of PGMEA, and 3.04 parts of dimethyl-2,2′-azobisisobutyrate(hereinafter referred to as DAIB), the monomer solution was addeddropwise in the flask at a fixed rate over 4 hours. Then, thetemperature was maintained at 80° C. for 3 hours.

Then, the resulting reaction solution was added dropwise in an about10-fold amount of a solvent mixture of methanol and water in a volumeratio of 8:2 to obtain a precipitate of a white precipitate (copolymerP-1). A wet powder obtained by filtering this precipitate was washed ina solvent mixture of methanol and water in a volume ratio of 9:1 in anamount which is about 10 times as much as that of the reaction solution.After washing, the precipitate was collected by filtration and thendried under reduced pressure at 60° C. for about 40 hours to obtain acopolymer P-1. Thermostability of the acetal structure of the resultingcopolymer P-1 was measured. The results are shown in Table 1.

Example 3 Synthesis of Methacrylate Represented by the Following Formula(A-2)

In a 1 L glass three-necked flask equipped with a stirrer, athermometer, and a reflux condenser tube, 69.0 g (0.50 mol) ofnorbornenecarboxylic acid, 129.0 g (1.5 mol) of methacrylic acid and 4.8g (0.05 mol) of methanesulfonic acid were charged and the temperaturewas raised to 130° C. while stirring. While maintaining the temperatureof the flask at 130° C., the reaction was conducted for 2 hours. Afterthe completion of the reaction, the reaction solution was cooled in anice bath and then 200 ml of toluene and 100 ml of water were added whilestirring. The solution was transferred to a separatory funnel and, afterremoving the aqueous layer, the toluene layer was concentrated to obtain110.0 g of a methacrylic acid adduct of the following formula (7).

110.0 g of the resulting methacrylic acid adduct represented by theformula (7) was charged in a 1 L glass three-necked flask equipped witha stirrer and a thermometer, and then 200 ml of dimethyl formamide and50.5 g of triethylamine were added, followed by stirring. Whilemaintaining the inner temperature at 25° C. under stirring, 40.2 g (0.5mol) of chloromethyl methyl ether was added dropwise over 2 hours usinga dropping funnel. After the completion of the dropwise addition andstirring at room temperature for one hour, 600 ml of toluene and 200 mlof water were added. The solution was transferred to a separatory funneland, after removing the aqueous layer, the toluene layer wasconcentrated. This concentrated solution was purified by distillationunder reduced pressure to obtain 96.6 g (0.36 mol) of a methacrylaterepresented by the formula (A-2).

Example 4 Synthesis of Copolymer P-2

In a flask equipped with a nitrogen introducing tube, a stirrer, acondenser and a thermometer, 185.3 parts of PGMEA was charged under anitrogen atmosphere and the temperature of a hot water bath was raisedto 80° C. while stirring. Using a dropping apparatus, a monomer solutionprepared by mixing 107.2 parts of a methacrylate represented by theformula (A-2), 68.0 parts of GBLMA, 47.2 parts of HAdMA, 333.6 parts ofPGMEA, 6.56 parts of 2,2′-azobisisobutyronitrile (hereinafter referredto as AIBN) and 1.75 parts of n-octylmercaptan (hereinafter referred toas nOM) was added dropwise in the flask at a fixed rate over 6 hours,followed by maintaining at 80° C. for one hour. Then, the resultingreaction solution was added dropwise in an about 30-fold amount ofmethanol with stirring to obtain a colorless precipitate (copolymerP-2). The resulting precipitate was filtered so as to remove theresidual monomer included in the precipitate and the precipitate waswashed in methanol in an amount which is about 30 times as much as thatof the monomer used in the polymerization. Then, the precipitate wascollected by filtration and dried under reduced pressure at 50° C. forabout 40 hours. Physical properties of the resulting copolymer P-2 wereevaluated. The results are shown in Table 1.

Example 5 Synthesis of Methacrylate Represented by the Following Formula(A-3)

110.0 g of a methacrylic acid adduct represented by the formula (7)obtained in the same manner as in Example 3 was charged in a 1 L glassthree-necked flask equipped with a stirrer and a thermometer and then200 ml of dimethyl formamide and 50.5 g of triethylamine were added,followed by stirring. While maintaining the inner temperature at 25° C.under stirring, 74.0 g (0.5 mol) of chloromethyl cyclohexyl ether wasadded dropwise over 3 hours using a dropping funnel. After thecompletion of the dropwise addition and stirring at room temperature forone hour, 600 ml of toluene and 200 ml of water were added. The solutionwas transferred to a separatory funnel and, after removing the aqueouslayer, the toluene layer was concentrated. The concentrated solution wasmixed with 0.5 g of powdered sodium hydroxide and then purified bydistillation under reduced pressure to obtain 107.5 g (0.32 mol) of amethacrylate represented by the above formula (A-3).

Example 6 Synthesis of Copolymer P-3

In the same manner as that in Example 3, except that the amount of PGMEAto be charged in the flask was 202.8 parts and a monomer solutionprepared by mixing 134.4 parts of a methacrylate represented by theformula (A-3), 68.0 parts of GBLMA, 41.0 parts of 5- or6-cyanobicyclo[2.2.1]heptyl-2-methacrylate (hereinafter referred to asCNNMA) represented by the following formula:

365.1 parts of PCMEA, 6.56 parts of AIBN, and 0.58 parts of nOM was usedas the monomer solution, a copolymer P-3 was obtained. Physicalproperties of the copolymer P-3 were evaluated. The results are shown inTable 1.

TABLE 1 Example 2 Example 4 Example 6 Copolymer P-1 P-2 P-3 Mass averagemolecular 25,000 8.00 11,000 weight (Mw) Molecular weight 3.19 1.60 1.77distribution (Mw/Mn) Composition A-1 40 — — ratio of monomer A-2 — 40 —unit in polymer A-3 — — 40 (mol %) GBLMA 40 40 40 HAdMA 20 20 — CNNMA —— 20 Heat stability index 0.52 0.96 0.89 of polymer

INDUSTRIAL APPLICABILITY

The polymer of the present invention is useful as a constituentcomponent resin of a positive resist. When the polymer of the presentinvention is used as a resist resin in DUV excimer laser lithography,electron beam lithography, or EUV lithography, it is possible to stablyform a fine resist pattern with high accuracy because of highsensitivity, high resolution, and excellent line edge roughness andtrailing.

1-6. (canceled)
 7. A copolymer comprising: a monomer represented by thefollowing formula (3):

wherein R represents a hydrogen atom or a methyl group, R¹ and R² eachindependently represents a hydrogen atom or an alkyl group having 1 to20 carbon atoms, or R¹ and R² are combined with each other to form aring structure, A¹ represents a single bond, alkylene, oxyalkylene,—C(O)O—, or —CH₂CH₂OC(O)—, A² represents a single bond, alkylene,oxyalkylene, —CO—; —C(O)O—, or —C(O)OCH₂CH₂—; and Z represents acyclohexane ring, norbornane ring, bicyclo[2.2.2]octane ring, ortetracyclo[4.4.0.1^(2,5)]dodecane ring, all of which may have asubstituent; and at least one monomer containing a lactone structure inthe molecule.
 8. A copolymer comprising: a monomer represented by thefollowing formula (3):

wherein R represents a hydrogen atom or a methyl group, R¹ and R² eachindependently represents a hydrogen atom or an alkyl group having 1 to20 carbon atoms, or R¹ and R² are combined with each other to form aring structure; A¹ represents a single bond, alkylene, oxyalkylene,—C(O)O—, or —CH₂CH₂OC(O)—, A² represents a single bond, alkylene,oxyalkylene, —CO—, —C(O)O—, or —C(O)OCH₂CH₂—, and Z represents acyclohexane ring, norbornane ring, bicycle[2.2.2]octane ring, ortetracyclo[4.4.0.1^(2,5)]dodecane ring, all of which may have asubstituent; and at least one monomer selected from the group consistingof: a monomer containing alicyclic skeleton having a hydroxy group and amonomer containing alicyclic skeleton having a cyano group.
 9. Acopolymer comprising: 25 to 70 mol % of a constituent unit representedby the following formula (1):

wherein R represents a hydrogen atom or a methyl group, R¹ and R² eachindependently represents a hydrogen atom or an alkyl group having 1 to20 carbon atoms, or R¹ and R² are combined with each other to form aring structure; A¹ represents a single bond, alkylene, oxyalkylene,—C(O)O—, or —CH₂CH₂OC(O)—, A² represents a single bond, alkylene,oxyalkylene, —CO—, —C(O)O—, or —C(O)OCH₂CH₂—, and Z represents acyclohexane ring, norbornane ring, bicyclo[2.2.2]octane ring, ortetracyclo[4.4.0.1^(2,5)]dodecane ring, all of which may have asubstituent; 25 to 70 mol % of a constituent unit derived from at leastone monomer containing a lactone structure in the molecule; and 5 to 20mol % of a constituent unit derived from at least one monomer selectedfrom the group consisting of: a monomer containing alicyclic skeletonhaving a hydroxy group and a monomer containing alicyclic skeletonhaving a cyano group.
 10. A resist composition comprising the copolymeraccording to claim
 7. 11. A resist composition comprising the copolymeraccording to claim
 8. 12. A resist composition comprising the copolymeraccording to claim
 9. 13. A pattern forming method comprising the stepsof: coating the resist composition according to claim 10 on ato-be-processed substrate, exposing the coated substrate to light havinga wavelength of 250 nm or less, and developing the exposed substrateusing a developing solution to form a pattern.
 14. A pattern formingmethod comprising the steps of: coating the resist composition accordingto claim 11 on a to-be-processed substrate, exposing the coatedsubstrate to light having a wavelength of 250 nm or less, and developingthe exposed substrate using a developing solution to form a pattern. 15.A pattern forming method comprising the steps of: coating the resistcomposition according to claim 12 on a to-be-processed substrate,exposing the coated substrate to light having a wavelength of 250 nm orless, and developing the exposed substrate using a developing solutionto form a pattern.